The present invention is related to a speed measurement method; especially to a speed measurement method using blurred images of objects for speed calculation of moving objects so that the cost of the speed detectors can be reduced.
In recent years, because of the advance on the development of various aircrafts, baseball exercise, and electrical devices, people are getting more interested in knowing the speed of flying objects, the pitching speed of sports players, and the speeding of vehicles detected by the law enforcement agencies. Due to the increasing demands of high quality products for speed detection, the development of speed measurement methods varies from traditional single-point measurement to digital image techniques nowadays. Thus, developing a novel, efficient, and low cost speed measurement method is an important issue for both consumer products and the systems used for police staffs.
Currently, most of speed measurement methods are based on Doppler effect. What is Doppler effect? When a fire truck is moving towards you, the sound's pitch is getting higher as the fire truck is close to you, and getting lower as the fire truck is away from you. This is the so-called Doppler effect. Take acoustic waves as another example, suppose the waves with wavelength λ, and frequency ƒ, are emitted from a source toward an observer, the stationary observer receives the acoustic waves with the frequency higher than ƒand the wavelength shorter than λ. That is, the pitch received by the observer is getting higher. On the other hand, as the source moves away from the observer, the observer receives the acoustic waves with the frequency lower than ƒ and the wavelength longer than λ, therefore the pitch is getting lower.
Refer to U.S. Pat. No. 5,814,732, a laser Doppler speed measuring apparatus is disclosed. The speed measuring method includes a laser detector and a demodulator. By a pulse with a fixed frequency emitted from the laser detector toward the motion object, the laser receives reflected pulse with higher or lower frequency according to the Doppler effect. The reflected pulse is then converted to electric signal and processed by the demodulator for the speed calculation of the moving object. One major drawback of this method is that the equipment used in the speed detector implementation is expensive. Moreover, they can be easily detected by anti-detection devices due to the continuously emitted pulse. Thus, this type of speed detectors when used for highway or local traffic speed law enforcement is easily detectable by electronic speed radar detectors.
Therefore, if a speed measurement method based on passive devices is provided, it will be a great advantage in terms of cost and usability of the speed detection apparatus.